President Donald Trump announced on Twitter Sunday afternoon that he was planning to officially demand an investigation into the FBI, Department of Justice, and Obama administration on Monday, following reports that the FBI used an informant to investigate Russian contacts within the Trump campaign.

If Trump follows through and orders the DOJ on Monday to launch an investigation, it would force the Justice Department to decide whether to follow Trump’s order, and could severely inflame tensions around the presidency and Russia investigation.

“I hereby demand, and will do so officially tomorrow, that the Department of Justice look into whether or not the FBI/DOJ infiltrated or surveilled the Trump Campaign for Political Purposes - and if any such demands or requests were made by people within the Obama Administration!” he Tweeted.

The message followed string of earlier Tweets attacking Robert Mueller’s investigation, criticizing the cost of the ongoing probe into his campaign’s potential collusion with Russia.

The last message also marked a possible turning point in Trump’s online criticism of the Justice Department if he does, in fact, ask the DOJ to investigate the FBI or the Obama administration on Monday.

Following the release of a New York Timesreport on Saturday alleging that Donald Trump Jr. had met with an emissary for Saudi Arabia and the United Arab Emirates during the 2016 campaign, Trump lashed out against the “long & boring story” on Twitter and asked when the “world’s most expensive witch hunt” would finally “STOP.”

“Things are really getting ridiculous. The Failing and Crooked (but not as Crooked as Hillary Clinton) @nytimes has done a long & boring story indicating that the World’s most expensive Witch Hunt has found nothing on Russia & me so now they are looking at the rest of the World!” Trump tweeted Sunday.

“At what point does this soon to be $20,000,000 Witch Hunt, composed of 13 Angry and Heavily Conflicted Democrats and two people who have worked for Obama for 8 years, STOP!” Trump added in a later tweet.

According to the New York Times report, Trump Jr. met with George Nader in August 2016, during a meeting in which Nader said that Saudi Arabia and the UAE were both eager to help Trump win the presidency. The meeting, which the Times noted has been a focus of Mueller’s probe, was also attended by Erik Prince, a Republican donor and private security contractor with ties to the Middle East, and Israeli social media specialist Joel Zamel, whose firm specialized in social media manipulation.

The Times reported that Trump Jr. responded “approvingly” to the nations’ offer to help the campaign, and Nader was embraced as a “close ally” by the campaign, suggesting that the campaign’s potential collusion with foreign nations could have gone beyond Russia. It is unknown, however, whether Nader’s proposal for Saudi Arabia and the UAE to assist the Trump campaign was ultimately executed.

In his Sunday tweets, the president then went on to criticize the investigation for its bias toward Democrats, questioning why the FBI had not looked into Hillary Clinton’s emails and why Democratic lobbyist Tony Podesta, who is reportedly under investigation by Mueller for his ties to former Trump campaign manager Paul Manafort, had not yet been charged and arrested.

“Now that the Witch Hunt has given up on Russia and is looking at the rest of the World, they should easily be able to take it into the Mid-Term Elections where they can put some hurt on the Republican Party,” Trump tweeted. “Don’t worry about Dems FISA Abuse, missing Emails or Fraudulent Dossier!”

The Mueller investigation marked its one-year anniversary this week, and despite Trump’s repeated claims it is no more than a “witch hunt,” it has already resulted in nearly two dozen indictments and several guilty pleas. It is unclear where Trump’s specific $20 million price tag for the probe comes from; according to a congressional budget cited by Politico, Mueller’s team is spending approximately $10 million per fiscal year on the investigation.